Hi Alex,
Your problem is that it’s a long way to travel to Morondava or Belo sur Tsiribihina only to be told that the trail from Belo to Bekopaka is no longer passable. Unless you have other things you want to do that will take you to the area, you’d be best advised to simply phone one or more of the hotels in Morondava listed in either the LP or Bradt guides. As they almost all organise trips to the Tsingy for their guests, they’ll be able to tell you whether they’re still running these trips and how long they expect to go on doing so. Obviously, you wouldn’t need to commit to booking one of their tours.
Other things that might take you to the area: Morondava itself has good beaches, there’s the Avenue des Baobabs, Kirindy Forest Reserve, by pirogue to Belo sur Mer for Kirindy Mitea National Park and of course the trip down the Tsiribihina.
By the way, when I was last there, the guides told me that if anyone ever managed to get to Bekopaka during the wet season, they’d take them into the Park. Just that no one’s ever done it yet.
Hope the weather is kind to you!